1) Field of the Invention
The present invention concerns an article made from overmoulded composite material and the relative preparation method.
2) Description of Related Art
The present invention originates in the technical field of containers made from composite material intended to contain products of the cosmetic, pharmaceutical, food and perfume industry, or for example to be used as tableware.
In the field of containers made from composite material, in particular composite materials consisting of glass or transparent or semi-transparent thermoplastic resins, for some time it is has been known to use the technique of jacket through overmoulding of two or more layers of the same material (glass/glass or resin/resin overmoulding).
The technique of jacket is used mainly with the purpose of obtaining aesthetic effects.
The material used to form the jacket, for example, can have colour, light refraction index or other properties different from those of the material of the container subjected to overmoulding. By suitably varying the properties of the overmoulded materials it is possible to create numerous aesthetic effects capable of attracting the interest of the user with regard to the article and its content.
The jacket of a container can be total or partial: in the first case, the jacket entirely covers the recipient body, i.e. the portion of the container normally intended to receive the content; in the second case, the jacket only covers a portion of the recipient body.
The jacket is made through injection overmoulding processes or by pressing. Overmoulding processes distinguish themselves from functional coating processes in that the thickness of the material applied onto the overmoulded container is much greater than that generally applied as functional coating. Typically, a functional coating has a thickness of the order of a few micrometres, whereas a jacket applied by injection overmoulding has a thickness that can vary from 1 millimetre up to 1-2 centimetres. Moreover, the material applied as functional coating generally does not contribute to the exterior appearance of the surfaces on which it is applied.
Functional coatings are applied through dipping in suitable liquid coating compositions or through spraying or electrospraying, spin coating, plasma, sol-gel, etc.
In the state of the art the jacket of a container is obtained through manual or automated processes.
An example of an automated industrial process for jacketing glass articles through overmoulding of thermoplastic resin is described in WO 02/094666 (WO'666). In particular, this document describes an overmoulding method suitable for making the jacket of glass or metal bottles with thin walls.
The method described in WO'666 and the products obtained with it have various drawbacks.
Firstly, the method is applicable exclusively to the overmoulding of glass articles in bottle form.
A second drawback is given by the fact that the layer of overmouldable resin has a minimum thickness equal to at least three times the minimum thickness of the walls of the glass container.
A third drawback is then linked to the overall weight of the article made from overmoulded composite material, which is lighter than a container made entirely from glass and having the same dimensions and shape. Although the reduction in weight has a favourable impact on the production and transportation costs of the finished articles, in the field of packaging of cosmetic and perfume products, however, the weight of the container is considered an important factor from the commercial point of view, since it has an influence on the perception of value of the content by the user.
The aforementioned drawbacks clearly limit the margins of creativity of those that design the aesthetic characteristics of these articles.
The overmoulding processes known in the prior art, such as that described in WO'666, can also have drawbacks concerning the reproducibility of the end product and the possible geometric shapes of the overmoulded containers. Indeed, the moulding is carried out using suitably shaped moulds, inside which the glass container is positioned. Inside the mould the container is subjected to the thrusting forces that the resin exerts on its walls and, therefore, it is easily subject to breaking. In order to at least partially avoid this problem, the state of the art is actually limited to overmould only glass containers having geometric shapes substantially without corners and/or with very rounded walls (typically containers shaped as solids of revolution), which can be produced in series with a smaller amount of waste due to the glass breaking in the injection step.
In line with these drawbacks of the state of the art, WO'666 also describes, as the preferred embodiment, overmoulding of glass containers having a substantially spherical shape.
The conditions at which it is possible to carry out overmoulding also have an influence over the characteristics of the jacket and, therefore, over the final appearance of the product. The thickness of the jacket that can be made through injection moulding, indeed, depends on the degree of fluidity of the resin and, therefore, on the temperature at which it is injected into the mould. In order to make low-thickness jackets it is necessary to have high-fluidity resins that can easily penetrate into the narrowest cavities of the mould. However, if the temperature of the resin is too high, its contact with the glass can damage it or even cause it to break. In WO'666 the injection temperature of the resin is within the range 120-160° C.